Categories and keywords tell Amazon which readers to show your book to. Wrong choices mean the right readers never see it.
Research first
List five books that readers of yours also buy. Open each one and note its categories and the words in its title and description. Repeat for a few more. The terms that appear again and again are the language your readers use.
Choose categories
KDP lets you pick up to three. Choose the closest fit first, then one or two narrower ones. Compare the competition: a category full of bestsellers is harder to appear in than a narrower one where a steady seller can rank. Pick categories your book truly belongs to, since misfiled books disappoint readers.
Choose keywords
Keywords are phrases a reader would type. Use specific phrases ("cozy mystery village bakery") rather than single broad words ("mystery"). Do not repeat words already in your title, and leave out your own name. Never use another author's name, a trademark or a claim like "bestseller", which KDP does not allow.
Check the rules
Run your title, subtitle and keywords through the metadata checker. It flags the length limits we have confirmed on KDP's pages and marks the ones we could not, so you know what to double-check in KDP itself.
Review on a schedule
Categories and reader phrases change. Check your choices every six months and after any change in sales. Keep notes of what you changed and when, so you can see what worked. Our categories and keywords article has more examples.